Probably because they look like candy, and they're packaged with food a lot?

Even if not packaged with food, these sachects left on the table while unboxing, e.g. a pair of shoes, might entice kids... And it's just easier to print "DO NOT EAT" rather than have separate production lines for "for shoes" and "for food".

Although, from the description, it seems they're perfectly safe (because they're inert) to eat...